It seems like, in your case, the publication is evidence that the rabbit hole was at least original and interesting. Students in that category tend to graduate, have a few compelling results to their name, and simply expend a couple extra semesters relative to the average.

The real question is whether they learn to focus efforts on the relevant goal (in which case, these original thinkers with innate curiosity can be fantastic hires) or continue their rabbit-hole-exploring ways (in which case they generate publications as post-docs, but generally struggle in the private sector where folks want THEIR questions answers ASAP). Which are you?

(Fascinating discussion!)